Leaky waveguide line

ABSTRACT

A leaky waveguide apparatus in which undesirable transmission modes caused by irregularities in the waveguide are eliminated. In one embodiment the unwanted transmission modes are eliminated by a section of helical waveguide, and power is extracted from the leaky waveguide by a converter, phase shifter, and auxiliary leaky waveguide. In another embodiment, the unwanted transmission modes are eliminated by tapered tube means and a directional coupler. The power is extracted from the leaky waveguide through the directional coupler, a phase shifter, and an auxiliary leaky waveguide.

Unite States Kitani et a1.

atent i 1 Jan. 23, 1973 [s41 LEAKY WAVEGUIDE LINE [75] Inventors: Hiroshi Kitani; Kenichi Yoshida; l-lideo Ohtsubo; Masataka Kuroda, all of Osaka, Japan [73] Assignee: Sumitamo Electric Industries, Ltd., Osaka, Japan [22] Filed: Dec. 23, 1970 [21] Appl.No.: 100,937

[30] Foreign Application Priority Data Dec. 25, 1969 Japan ..45/1632 [52] US. Cl. ..333/84 R, 343/771, 333/95 R, 333/98 M [51] Int. Cl. ..H01q 13/00, 1104b 7/00, H04b 3/60 [58] Field of Search ..333/95 S, 98 M, 29, 31,10", 246/30; 343/771 [56] References Cited UNITED STATES PATENTS 2,921,979 iTi'dWiafiieki .."......'l.-.' .sssissx 3,609,675 9/1971 Ab6l ..246/3O X 3,281,591 10/1966 Takeya ..246/30 X 2,580,155 12/1951 Brannen ..340/25S C 2,759,156 8/1956 Younker ..343/776 Primary Examiner-Eli Lieberman Assistant ExaminerMarvin Nussbaum Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT 7 Claims, 2 Drawing Figures LEAKY WAVEGUIDE LINE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a leaky waveguide line.

2. Description of the Prior Art In a leaky waveguide, or coaxial cable, holes and slots are provided in the coaxial cable or circular waveguide such that part of energy of the electromagnetic wave propagated inside the waveguide is leaked outside through the holes. It has been proposed that such waveguide lines be installed over long distances to be utilized for train communications and mobile communications. According to this concept, a leakage line such as a leaky waveguide, a leaky coaxial cable, etc. is arranged so that the leaked wave is concentrated in the vicinity of the transmission line. In this manner information can be effectively exchanged with a moving train along the transmission line.

A circular leakage waveguide line using TE mode is a low loss transmission system which is efficient for mobile communications systems. However, the TE mode propagated inside the tube is strongly affected by even small geometrical irregularities in the waveguide. The irregularities may be a continuous change in the shape of waveguide (winding, bend, change from circular to elliptic form, etc.), or discontinuous changes in the shape at the waveguide connection part (tilt, offset, diameter changes, etc.) when the frequency range is of centimeter wavelength or millimeter wavelength (socalled super or extremely high frequency region). The effect of the irregularities may be modes conversion in which TE, mode is converted into another unwanted mode. This mode conversion acts to lower the quality of the transmission signal. For example, delay distortion is produced in the transmission signal. Particularly in the low loss transmission of long distances, the mode conversion seriously affects the transmission quality. To overcome mode conversion the converted mode must be absorbed by mode filters as much as possible. To overcome mode conversion in prior art systems a helical waveguide having holes, slits or the like operates as the mode filter, and is inserted into the leaky waveguide line.

According to these prior art devices, however, the radiation loss of the leaky wave is varied due to the lossy layer in the wall of the tube of the leaky helical waveguide. Furthermore, it is difficult to accurately cut the slits in the helix. As a result, uniform receiving levels cannot be obtained at an antenna.

SUMMARY OF THE INVENTION This invention has been proposed to eliminate the foregoing disadvantages inherent to the prior art. The principal object of this invention is to provide a leaky waveguide line in which a mode filter such, as a helical waveguide having no leaky holes or a tapered tube, is inserted at an arbitrary section in the leakage waveguide line. The coupling between a train antenna and a leaky waveguide line is realized uniformly and furthermore, the unwanted mode raised in the waveguide line is eliminated by the combining use of auxiliary leaky waveguide provided with leaky holes and the helical waveguide with no such holes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a preferred embodiment of the present invention.

FIG. 2 is another preferred embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1, 1 and 1' are circular leaky waveguides. A mode filter 2 consisting of a helical waveguide, a dielectric lining waveguide, etc., having no leaky structure in order to absorb unwanted modes raised in the waveguide is inserted between circular leaky waveguides 1 and 1 in an arbitrary section of the leaky waveguide line. An example of a well known helical waveguide is one whose inner wall is provided circumferentially with thin wires which absorb effectively unwanted modes, especially TM mode. Three is an auxiliary leaky waveguide radiating a leaked wave which is at a uniform receiving level at the extractor means including a mode filter. An circular to rectangular converter 6 is disposed atthe wall of the circular leaky waveguide 1. This converter 6 is to extract a part of the transmitted wave energy and supply it to the auxiliary waveguide 3 via the attenuator 4 and phase shifter 5. Most of the power is transmitted to the next leaky waveguide 1' via a mode filter 2, from the leaky waveguide l. The extractor means also includes attenuator 4 and phase shifter 5 are amplitude and phase adjusting circuits to prevent variations in the antenna receiving level due to interference by the leaky wave from the leaky waveguides 1 and 1 and from the auxiliary leaky waveguide 3. Thus the attenuator 4 and phase shifter 5 serve to maintain a uniform antenna receiving level. Seven is a resistive terminator.

As mentioned above, when a train antenna pass through in the vicinity of a mode filter 2 with no leaky structure, the uniform coupling level between a train antenna and a leaky waveguide is maintained by the leaked wave from the auxiliary leaky waveguide 3.

FIG. 2 shows another embodiment of the invention, wherein part of the transmitted power is fed to an auxiliary leaky waveguide 3 through an extractor means including a tapered tube 12 circular to rectangular converter 6, directional coupler 8 and phase shifter 5. The remainder of the power is supplied to a subsequent leaky waveguide 1' via directional coupler 8, phase shifter 5, circular to rectangular converter 6 and tapered tube 12. Five is a phase shifter, 6 is a circular to rectangular converter converting the T13 mode to the TE mode and 7 is a resistive terminator. The tapered tube 12 eliminates the unwanted transmission modes. The size of the leaky hole in the next stage is designed to obtain a uniform receiving level. Phase shifter 5 compensates for the phase shift caused by the additional electrical distance of the apparatus inserted between sections 1 and 1' through which the transmitted wave in the system must travel.

As has been pointed out, the invention has its principal feature in that the receiving level is held uniformed by compensating the phase shift through the arrangement, wherein the size of the hole in the leaky waveguide in a next stage is suitably adjusted and a phase shifter is utilized. This is realized without using amplifiers in its circuit. Furthermore, a flexible waveguide can be used so that the leaky waveguide line can be bent at an arbitrary angle. In a train communication system, for example, use of flexible waveguide is particularly advantageous when installing a transmission line in a station area where a bent line is often necessary.

While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. A leaky waveguide apparatus comprising:

a. a leaky waveguide line;

b. mode filter means inserted in said leaky waveguide line for removing unwanted transmission modes of the transmitted power in said leaky waveguide line; extracting means for extracting part of the transmitted power from said leaky waveguide line; and d. auxiliary leaky waveguide means, said auxiliary leaky waveguide means coupled to said extracting means for receiving said extracted power, whereby the level of power from said auxiliary leaky waveguide means is uniform with respect to said leaky waveguide line because said unwanted transmission modes have been removed by said mode filter means ad interference between leaked waves from said leaky waveguide line and said auxiliary waveguide means means has been eliminated by said extracting means.

2. The apparatus of claim 1, wherein said extracting means includes a phase shifter for compensating for phase shifts in a wave travelling through the apparatus.

3. The apparatus of claim 1, wherein said extracting means includes:

a. a converter waveguide line;

an attenuator coupled to said converter means; and a phase shifter coupled to said attenuator and to said leaky waveguide means wherein said attenuator and phase shifter prevent variation in the level of power out of said apparatus due to interference of waves from said leaky waveguide line and said auxiliary leaky waveguide means.

4. The apparatus of claim 1, wherein said mode filter means for removing unwanted transmission modes includes a helical waveguide coupled between two sections of leaky waveguide lines.

5. The apparatus of claim 1, wherein said extracting means includes:

A. a directional coupler connected to said leaky waveguide line, and

b. phase shifter means coupled to said directional coupler.

6. The apparatus to claim 1, wherein said mode filter means for removing unwanted transmission modes includes a tapered tube means and a directional coupler.

7. The apparatus of claim 6, wherein said mode filter means for removing unwanted transmission modes further includes flexible waveguide means coupled to said tapered tube means.

means coupled to said leaky 

1. A leaky waveguide apparatus comprising: a. a leaky waveguide line; b. mode filter means inserted in said leaky waveguide line for removing unwanted transmission modes of the transmitted power in said leaky waveguide line; c. extracting means for extracting part of the transmitted power from said leaky waveguide line; and d. auxiliary leaky waveguide means, said auxiliary leaky waveguide means coupled to said extracting means for receiving said extracted power, whereby the level of power from said auxiliary leaky waveguide means is uniform with respect to said leaky waveguide line because said unwanted transmission modes have been removed by said mode filter means ad interference between leaked waves from said leaky waveguide line and said auxiliary waveguide means means has been eliminated by said extracting means.
 2. The apparatus of claim 1, wherein said extracting means includes a phase shifter for compensating for phase shifts in a wave travelling through the apparatus.
 3. The apparatus of claim 1, wherein said extracting means includes: a. a converter means coupled to said leaky waveguide line; b. an attenuator coupled to said converter means; and c. a phase shifter coupled to said attenuator and to said leaky waveguide means wherein said attenuator and phase shifter prevent variation in the level of power out of said apparatus due to interference of waves from said leaky waveguide line and said auxiliary leaky waveguide means.
 4. The apparatus of claim 1, wherein said mode filter means for removing unwanted transmission modes includes a helical waveguide coupled between two sections of leaky waveguide lines.
 5. The apparatus of claim 1, wherein said extracting means includes: A. a directional coupler connected to said leaky waveguide line, and b. phase shifter means coupled to said directional coupler.
 6. The apparatus to claim 1, wherein said mode filter means for removing unwanted transmission modes includes a tapered tube means and a directional coupler.
 7. The apparatus of claim 6, wherein said mode filter means for removing unwanted transmission modes further includes flexible waveguide means coupled to said tapered tube means. 